The present disclosure relates to methods and treatments used in conjunction with subterranean fracturing treatments, and more specifically, to methods involving the sequential application of surfactants to improve fluid recovery and control fluid loss in conjunction with those treatments.
Fracturing treatments are commonly used in subterranean operations, among other purposes, to stimulate the production of desired fluids (e.g., hydrocarbons, water, etc.) from a subterranean formation. For example, hydraulic fracturing treatments generally involve pumping a treatment fluid (e.g., a fracturing fluid) into a well bore that penetrates a subterranean formation at a sufficient hydraulic pressure to create or enhance one or more cracks, or “fractures,” in the subterranean formation. “Enhancing” one or more fractures in a subterranean formation, as that term is used herein, is defined to include the extension or enlargement of one or more natural or previously created fractures in the subterranean formation. The creation and/or enhancement of these fractures, among other things, may enhance the flow of fluids through the subterranean formation so that they may be produced out of the subterranean formation (e.g., into and out of a well bore penetrating at least a portion of the subterranean formation) more readily. Such fracturing treatments also may be performed in combination with other subterranean treatments useful in the particular formation, such as gravel packing and/or acidizing treatments, which may be referred to as “frac-packing” and “frac-acidizing” treatments, respectively.
Providing effective fluid loss control in subterranean fracturing treatments is often desirable. “Fluid loss,” as that term is used herein, refers to the undesirable migration, leak off, or other loss of fluids (e.g., a fracturing fluid) into a subterranean formation and/or a proppant pack. The loss of fracturing fluid into the formation during a fracturing operation may result in a reduction in fluid efficiency, such that the fracturing fluid cannot propagate the fracture as desired. In carrying out subterranean fracturing treatments, recovery of the fracturing fluid out of the formation also may be critical once the fracturing treatment has been completed, among other reasons, so that hydrocarbons and/or other fluids can flow more freely through the fractured zone and out of the well bore. Aqueous-based fracturing fluids also may cause high capillary pressures in the formation matrix, which may restrict the flow of produced hydrocarbons. Capillary pressures of several thousand psi may result in low permeability formations when water is introduced, wherein the high pressure differential needed to initiate the fluid flow may result in extended fluid recovery times, long term losses in the relative permeability to gaseous hydrocarbons, and long term loss of effective fracture half length.
In conventional treatments, surfactants may be added to the fracturing fluid(s) used during a subterranean fracturing treatment in order to reduce interfacial tensions between oil and water in the formation, reduce capillary pressure in the formation matrix, and facilitate flow in the fractures. However, these conventional methods often involve applying the surfactant throughout the entire fracturing treatment, which may require large amounts of those components that are often wasted due to fluid loss or inefficient treatment of the formation. Hydrocarbon fluids such as diesel or kerosene also may be added to fracturing fluids to reduce fluid leak off into the formation and facilitate flow. However, these hydrocarbon additives may introduce undesirable environmental properties and safety hazards, form undesired emulsions, damage formations, and/or their use may be prohibited in certain parts of the world.
While the present disclosure is susceptible to various modifications and alternative forms, specific example embodiments have been shown in the figures and are herein described in more detail. It should be understood, however, that the description of specific example embodiments is not intended to limit the invention to the particular forms disclosed. On the contrary, this disclosure is to cover all modifications and equivalents as illustrated, in part, by the appended claims.